The number of Indian Country crimes the U.S. Justice Department chose to prosecute has plateaued in recent years, according to federal statistics released this week. This despite efforts to boost public safety and prosecutions of sexual assault and other crimes.

An annual report obtained by The Associated Press showed U.S. Attorneys declined to prosecute 37 percent of the Indian Country cases they received last year. They said they dropped most of the cases for a lack of evidence. New Mexico Sen. Tom Udall said limited data collection and lack of clear protocols for authorities hold up many investigations.

"On Navajo Nation we have criminal investigators partnering with the FBI," Crotty said. "What they need is of course more personnel, highly trained personnel. There's been a steady number of Navajo Nation investigators but there's been an increase in crimes they're investigating."

Crotty said the Navajo Nation is still seeing high rates of sexual assault. A quarter of the cases U.S. Attorneys declined were sexual assault cases.

Trent Shores, who is Choctaw and a U.S. Attorney, said federal prosecutors declined to take some of the cases because they were sent to tribal courts, which shows some tribes' ability to handle cases at a local level.